fix(bzlmod): ensure that config_settings are generated for all available versions

I think that bazel-contrib#2253 has introduced an issue that went unnoticed because
we did not have an integration test checking this. The main issue is
that config settings of `is_python_3.x.y` were being generated only for
registered toolchains and that is not necessarily the desired behaviour
-- we may want to use the config settings for more values, so coupling
that was a mistake.

Author: aignas

python/private/python.bzl

@@ -241,6 +241,7 @@ def _python_impl(module_ctx):
         # Last toolchain is default
         default_python_version = py.default_python_version,
         minor_mapping = py.config.minor_mapping,
+        python_versions = list(py.config.default["tool_versions"].keys()),
         toolchain_prefixes = [
             render.toolchain_prefix(index, toolchain.name, _TOOLCHAIN_INDEX_PAD_LENGTH)
             for index, toolchain in enumerate(py.toolchains)